Wireless Telegraphy and Telephony

WIRELESS TELEGRAPHY 109 The vibrations or disturbances set up in the air by a sound emitting body are known as sound waves. These waves consist of a series of condensations and rarefactions TUNING FORK Fig. 124.—Method of registering vibrations of a tuning fork. succeeding each other at regular intervals, each air particle swinging to and fro in a very short path. Air waves cannot be seen by the naked eye, but their nature may be easily represented or illustrated. Fig. 126 Fig. 125.—Wavy line made by a bristle attached to a tuning fork prong in vibration when passed over smoked glass. gives a pictorial representation of the crowding together of the air particles during the passage of a wave. The loudness of the sound depends upon the amount and sud- denness of the change in pressure, and the note or pitch on the number of complete to and fro motions of the par- ticles per second. The timbre of a sound or the quality that distinguishes the note of a violin from that of a piano depends upon the